Dielectric covered electrostatic chuck

ABSTRACT

An electrostatic chuck  100  useful for holding a substrate  55  in a high density plasma, comprises an electrode  110  at least partially covered by a semiconducting dielectric  115 , wherein the semiconducting dielectric  115  may have an electrical resistance of from about 5×10 9  Ωcm to about 8×10 10  Ωcm.

CROSS-REFERENCE

This application is a divisional of U.S. patent application Ser. No.08/965,690, filed on Nov. 6, 1997, now U.S. Pat. No. 6,108,189, entitled“Electrostatic Chuck Having Improved Gas Conduits,” by Weldon et al.,which is a continuation-in-part of U.S. patent application Ser. No.08/639,596, filed on Apr. 26, 1996, now U.S. Pat. No. 5,720,818,entitled, “Conduits for Flow of Heat Transfer Fluid to the Surface of anElectrostatic Chuck,” by Weldon et al., both of which are incorporatedherein by reference in their entireties.

BACKGROUND

The present invention relates to an electrostatic chuck for holdingsubstrates in a process chamber.

Electrostatic chucks are used to hold substrates in variousapplications, including for example, holding a silicon wafer in aprocess chamber during semiconductor fabrication. A typicalelectrostatic chuck comprises an electrode covered by an insulator ordielectric layer. When the electrode of the chuck is electrically biasedwith respect to the substrate by a voltage, an attractive electrostaticforce is generated that holds the substrate to the chuck. In monopolarelectrode chucks, an electrically charged plasma above the substrateinduces electrostatic charge in the substrate that electrostaticallyholds the substrate to the chuck. A bipolar electrode chuck comprisesbipolar electrodes that are electrically biased relative to one anotherto provide the electrostatic attractive force.

With reference to FIGS. 1a and 1 b, the electrostatic attractive forcegenerated by electrostatic chucks 10 a, 10 b can be of different types.As schematically illustrated in FIG. 1a, a dielectric layer 11 with ahigh electrical resistance results in the generation of coulombicelectrostatic forces from the accumulation of electrostatic charge inthe substrate 12 and in the electrode 13 of the chuck 10 a. Thecoulombic electrostatic force is described by the equation:$F = {\frac{1}{2}\quad \varepsilon_{0}{\varepsilon_{r}\left( \frac{V}{t} \right)}^{2}}$

where ∈_(o) and ∈_(r) are the dielectric constant of vacuum and relativedielectric constant of the dielectric layer 11, respectively, V is thevoltage applied to the electrode 13, and t is the thickness of thedielectric layer. The electrostatic force increases with increasedrelative dielectric constant ∈_(r) of the dielectric layer 11.

With reference to FIG. 1b, Johnsen-Rahbek electrostatic attractionforces occur when an interface 14 of a low resistance dielectric layer15 and the substrate 12 comprises an interfacial contact resistance muchgreater than the resistance of the dielectric layer 15, i.e., when theresistance of the dielectric layer 15 from about 10¹¹ to about 10¹⁴ Ωcm.In these chucks, free electrostatic charge drifts through the dielectriclayer 15 under the influence of the electric field and accumulates atthe interface of the dielectric layer 15 and the substrate 12, asschematically illustrated in FIG. 1b. The charge accumulated at theinterface generates a potential drop represented by the equation:$F = {\frac{1}{2}\quad {\varepsilon_{0}\left( \frac{V}{\delta} \right)}^{2}}$

where δ denotes the contact resistance of the air gap 14 between thesubstrate 12 and the low resistance dielectric layer 15. TheJohnsen-Rahbek electrostatic attractive force is much larger for anapplied voltage than that provided by coulombic forces because (i)polarization in the dielectric layer 15, and (ii) free charges at theinterface 14 (which have a small separation distance from theaccumulated charges in the substrate) combine to enhance electrostaticforce. A strong electrostatic force securely clamps the substrate 12onto the chuck and improves thermal transfer rates. Also, it isdesirable to operate the chuck using lower voltages to reduce charge-updamage to active devices on the substrate 12.

It is known to use ceramic layers to fabricate the low conductivityJohnsen-Rahbek electrostatic chucks. For example, various formulationsof Al₂O₃ doped with low levels of 1-3 wt % TiO₂ to form low resistanceceramic layers are disclosed in Watanabe et al., “Relationship betweenElectrical Resistivity and Electrostatic Force of Alumina ElectrostaticChuck,” Jpn. J. Appl. Phys., Vol. 32, Part 1, No. 2, 1993; and“Resistivity and Microstructure of Alumina Ceramics Added with TiO₂Fired in Reducing Atmosphere,” J. of the Am. Cer. Soc. of Japan Intl.Edition, Vol. 101, No. 10, pp. 1107-1114 (July 1993). In anotherexample, U.S. Pat. No. 4,480,284 discloses a chuck having a ceramicdielectric layer made by flame spraying Al₂O₃, TiO₂, or BaTiO₃ over anelectrode and impregnating the pores of the ceramic layer with apolymer. Whereas pure Al₂O₃ ceramic has a resistivity on the order of1×10¹⁴ ohm cm, the alumina/(1-3 wt % titania) ceramic formulationstypically have lower resistivities on the order of 1×10¹¹ to 1×10¹³, andconsequently are more suitable for fabricating Johnsen-Rahbekelectrostatic chucks. However, one problem with such ceramic layers isthat the volume resistivity of the ceramic decreases to low values withincreasing temperature, which results in large current leakages thatexceed the capacity of the chuck power supply.

Another problem with low resistance ceramic formulations is their lowcharge accumulation and dissipation response time, i.e., the speed atwhich electrostatic charge accumulates or dissipates in the chuck. Thecharge accumulation time is the time to reach electrostatic chargesaturation and depends on the resistivity of the dielectric layer.Typical resistivities of conventional ceramics of greater than 1×10¹²Ωcm result in relatively slow charging times, often as high as 5 to 10seconds. The high resistance also results in a slow dechucking time,which is the time it takes for the electrostatic charge accumulated inthe chuck to dissipate after the voltage applied to the electrode isturned off. It is desirable for the chuck to provide rapid chucking anddechucking to provide high process throughput.

Yet another problem with conventional electrostatic chucks occurs duringtheir use in semiconductor processes that use plasma environments and,in particular, high density plasma environments. A plasma is anelectrically conductive gaseous medium formed by inductively orcapacitively coupling RF energy into the process chamber. High densityplasmas which are generated using a combined inductive and capacitivecoupling source typically comprise a thin plasma sheath having a largenumber per unit volume of energetic plasma ions. The high density plasmaspecies permeate into the interfacial gap between the substrate and thechuck, or the potential differences at the backside of the substratecause formation of glow discharges and electrical arcing at the backsideof the substrate. It is desirable to have an interfacial region that ismore resistant to plasma permeation and that can reduce plasma formationeven when charged plasma species penetrate into the gap.

The formation of glow discharges and arcing at the interfacial gap belowthe substrate causes additional problems when the substrate is cooled orheated by a heat transfer gas, such as helium, supplied to the interfacebetween the chuck and the substrate via channels in the body of thechuck. The heat transfer gas serves to enhance thermal heat transferrates. However, the pressure of the heat transfer gas below thesubstrate counteracts and reduces the electrostatic clamping forceexerted on the substrate. Because the semiconductor plasma processing istypically carried out at low pressures, the helium gas pressureincreases the size of the interfacial gap below the substrate, causingincreased permeation and penetration of the high density plasma into thegap. Additional problems occur when the heat transfer gas passes throughgas holes in the chuck that are surrounded by the electrode of the chuckwhich is supplied by a high power AC voltage. Instantaneous changes inpotentials can ionize the heat transfer gas adjacent to the gasdistribution holes, particularly when the diameter of the gas hole isrelatively large and provides a long mean free path which allowsavalanche breakdown of gas molecules in the gas holes. Ceramic chuckstypically have large diameter gas holes because it is difficult to drillsmall holes having diameters less than 0.5 mm because the ceramic at theedges of the holes shatters or chips off during drilling. Arcing andglow discharges within these large diameter gas holes in ceramic chuckscause deterioration of the regions adjacent to the gas distributionholes, including the adjacent dielectric layer and overlying substrate.

Thus, there is a need for an electrostatic chuck that reduces plasmaglow discharges and arcing in the interfacial gap between a substrateand chuck, particularly when heat transfer gas is provided to theinterface. There is also a need for an electrostatic chuck thatdeactivates or prevents plasma formation at the gas feeding apertures inthe chuck. There is a further need for a chuck having a low conductivitydielectric covering or enclosing the electrode which provides higherelectrostatic clamping forces, rapid chucking and dechucking responsetimes, and controlled leakage of current from the electrode.

SUMMARY

In one aspect of the present invention, an electrostatic chuck comprisesan electrode and a semiconducting dielectric which covers at least aportion of the electrode, the semiconducting dielectric having anelectrical resistance of from about 5×10⁹ Ωcm to about 8×10¹⁰ Ωcm.

In another aspect of the invention, a substrate processing chambercomprises a gas distributor adapted to introduce process gas in thechamber and a semiconducting dielectric covering an electrode, thesemiconducting dielectric having a receiving surface adapted to receivea substrate and the semiconducting dielectric having an electricalresistance of from about 5×10⁹ Ωcm to about 8×10⁹ Ωcm, and a plasmagenerator.

In another aspect of the invention, an electrostatic chuck comprises anelectrode and a semiconducting dielectric covering at least a portion ofthe electrode, the semiconducting dielectric comprising a surface toreceive a substrate, and the semiconducting dielectric having aresistivity sufficiently low to allow an electrical charge applied tothe electrode to leak from the electrode and accumulate as electrostaticcharge in the semiconducting dielectric, sufficiently high to retain theaccumulated electrostatic charge in the semiconducting dielectric duringprocessing of the substrate. A substrate may thereby beelectrostatically held to the semiconducting dielectric.

In another aspect of the invention, an electrostatic chuck comprises anelectrode, a first dielectric covering at least a portion of theelectrode and a second dielectric covering at least a portion of theelectrode.

In another aspect of the invention, a process for forming anelectrostatic chuck comprises mounting an electrode in a facingrelationship to a plurality of arcing electrodes, forming an arc betweenthe arcing electrodes, flowing a gas stream through the arc, andspraying a dielectric material into the gas stream. The sprayeddielectric material impinges on the electrode to form a dielectric layeron the electrode.

DRAWINGS

These features, aspects, and advantages of the present invention willbecome better understood with regard to the following description,appended claims, and accompanying drawings which illustrate versions ofthe invention, where:

FIG. 1a (Prior Art) is a schematic view of an electrostatic chuck thatoperates by coulombic electrostatic forces;

FIG. 1b (Prior Art) is a schematic view of an electrostatic chuck thatoperates by Johnsen-Rahbek electrostatic forces;

FIG. 2 is a schematic side view of a process chamber comprising anembodiment of the electrostatic chuck of the present invention;

FIG. 3a is a schematic side view of an electrostatic chuck comprising aunitary body of dielectric material enclosing an electrode and havinggas flow conduits extending therethrough;

FIG. 3b is a schematic top view of the chuck of FIG. 3a showing theoutlet of the conduits;

FIG. 4a is a schematic top view of an electrostatic chuck comprising gasflow conduits in grooves on the surface of the chuck;

FIG. 4b is a schematic sectional side view of another version of theelectrostatic chuck showing the dielectric member with gas flow conduitsand electrical isolators;

FIG. 5a is a perspective partial sectional view of an annular ring whichcan be used to form the gas flow channel and gas flow conduits in thechuck;

FIG. 5b is a sectional side schematic view showing an electricalisolator comprising dielectric coatings on a gas flow conduit in theannular ring of FIG. 5a;

FIG. 5c is a sectional side schematic view showing an electricalisolator comprising a dielectric insert in a gas flow conduit in theannular ring of FIG. 5a;

FIG. 5d is a sectional side schematic view showing an electricalisolator comprising a porous plug of dielectric material in a gas flowconduit in the annular ring of FIG. 5a;

FIGS. 6 and 7 are schematic side views showing fabrication of electricalisolators that comprise dielectric inserts fitted in the gas flowconduits;

FIG. 8a is a schematic side view showing a dielectric insert havingmultiple openings in a gas flow conduit;

FIG. 8b is a schematic side view showing a dielectric insert made of aporous material in a gas flow conduit;

FIG. 8c illustrates three hole patterns that can be used in thedielectric inserts of FIGS. 8a and 8 b;

FIG. 8d is a schematic side view of a composite dielectric insertcomprising a non-porous dielectric sleeve surrounding a porousdielectric center;

FIG. 8e is a top view of the composite dielectric insert of FIG. 8d;

FIG. 8f is a schematic side view of a porous dielectric insertpositioned in a gas flow conduit;

FIG. 9a is a schematic side view of a composite electrical isolatorcomprising a non-porous dielectric sleeve surrounding a porousdielectric center, with an annular gas flow opening therebetween;

FIG. 9b is a schematic side view of a composite electrical isolatorcomprising a ceramic core and a polymer sleeve;

FIG. 9c is a schematic side view of a composite electrical isolatorcomprising a tubular insert and an outwardly extending spacer ledge;

FIG. 10a is a schematic side view of a composite electrical isolatorcomprising a tapered non-porous dielectric sleeve surrounding a porousdielectric center;

FIG. 10b is a schematic side view of another version of a compositeelectric isolator;

FIG. 11 is a schematic side view of an electrical isolator comprising anembedded electrical lead;

FIGS. 12a through 12 f illustrate a method of forming an electricalisolator in a gas flow conduit;

FIGS. 13a through 13 c are schematic sectional side views showingfabrication of an electrical isolator comprising a tapered porous plugin a gas flow conduit;

FIG. 13d is a partial sectional perspective view of an electrostaticchuck fabricated according to FIGS. 13a through 13 c;

FIG. 14 is a schematic side view of an electrical isolator comprisingporous material covered by dielectric;

FIG. 15 is a schematic side view of the electrostatic chuck comprising acomposite dielectric layer having a first dielectric layer (such as asemiconducting dielectric) covering a central portion of the electrode,and a second dielectric layer (such as an insulator or dielectric)covering a peripheral portion of the electrode;

FIG. 16 is a schematic view of a plasma glow discharge sprayingapparatus;

FIG. 17 is a schematic view of a detonation gun flame spray apparatus;

FIG. 18 is a schematic view of an electrode arc spraying apparatus; and

FIG. 19 is a schematic sectional view of a preferred grain structure ofa semiconducting dielectric layer formed on an electrode using theapparatus of FIG. 18.

DESCRIPTION

The present invention relates to an electrostatic chuck that exhibitsreduced plasma glow discharges and electrical arcing at the interface ofthe substrate and chuck and provides fast chucking and dechuckingresponse times. The electrostatic chuck is described in the context ofholding substrates in a process chamber, as illustrated in FIG. 2. Theprocess chamber 50 schematically represents an “HDP” decoupled plasmachamber commercially available from Applied Materials Inc., Santa Clara,Calif., and described in commonly assigned patent application Ser. No.07/941,507, filed on Sep. 8, 1992, now abandoned which is incorporatedherein by reference in its entirety. The particular embodiment of theprocess chamber 50 is suitable for plasma processing of semiconductorsubstrates 55; however, the present invention can also be used withother process chambers or in other processes without deviating from thescope of the invention.

The process chamber 50 includes a process gas source 60 that feeds a gasdistributor 62 for introducing process gas into the chamber 50 and athrottled exhaust 65 for exhausting gaseous byproducts. A plasma isformed from the process gas using a plasma generator that couples RFenergy into the chamber, such as an inductor coil 70 adjacent to theprocess chamber 50 powered by a coil power supply 75. The chamber alsoincludes cathode and anode electrodes 80, 85 that capacitively coupleenergy into the chamber 50. The frequency of the RF voltage applied tothe cathode and anode 80, 85 and/or the inductor coil 70 is typicallyfrom about 50 Khz to about 60 MHZ, and more typically about 13.56 MHZ;and the power level of the RF voltage/current applied to the coil orprocess electrodes is typically from about 100 to about 5000 Watts.

An electrostatic chuck 100 is used to hold a substrate 55 for plasmaprocessing in the process chamber 50. In one version, the electrostaticchuck 100 comprises an electrode 110 covered by, and more preferablyembedded in, a dielectric member 115 that electrically isolates theelectrode from the substrate. The electrode 110 embedded in thedielectric member 115 provides increased electrical isolation from theplasma environment. Optionally, a base 105 supports the chuck, and aheat transfer fluid circulator 88 circulates heat transfer fluid throughthe channels 90 in the base to transfer heat to or from the chuck 100.In another version, shown for example in FIG. 3a, the chuck 100 isformed by a dielectric member 115 comprising a layer of dielectricmaterial covering a metal plate that serves as the electrode 110. By“dielectric member” 115 it is meant both the dielectric layer coveringthe electrode 110 and the unitary dielectric member having the electrode110 embedded therein.

Referring to FIG. 2, to operate the chuck 100, the process chamber 50 isevacuated to a low pressure, and a robot arm (not shown) transports asubstrate 55 from a load-lock transfer chamber through a slit valve intothe chamber 50. A lift finger assembly (not shown) has lift fingers thatare elevated through the chuck 100 by a pneumatic lift mechanism. Therobot arm places the substrate 55 on the tips of the lift fingers, andthe pneumatic lift mechanism, under the control of a computer system,lowers the substrate onto the chuck 100. After the substrate is placedon the chuck 100, the electrode 110 of the chuck is electrically biasedwith respect to the substrate 55 by a chuck voltage supply 120 toelectrostatically hold the substrate. After process completion, thepneumatic lift mechanism raises the lift pins to raise the substrate 55off the chuck 100, allowing the substrate to be removed by the roboticarm. Before raising the lift pins, the substrate 55 can be electricallydecoupled or dechucked by dissipating the residual electrical chargesholding the substrate to the chuck (after the voltage to the electrodeis turned off) by grounding the electrode 110 and/or substrate 55.

In the embodiment shown in FIGS. 3a and 3 b, the chuck comprises amonopolar electrode 110 embedded in, or covered by, the dielectricmember 115. The electrode 110 comprises a metal layer composed ofcopper, nickel, chromium, aluminum, molybdenum, or combinations thereof;that typically has a thickness of from about 1 μm to about 100 μm, andmore typically from 1 μm to 50 μm. For a substrate 55 having a diameterof 200 to 300 mm (6 to 8 inches), the electrode 110 typically comprisesan area of about 50 to about 250 sq. cm. In operation, a voltage appliedto the monopolar electrode 110 causes electrostatic charge to accumulatein the electrode (or in the dielectric member 115 covering the electrode110 for Johnsen-Rahbek chucks). The plasma in the chamber 50 provideselectrically charged species of opposing polarity which accumulate inthe substrate 55. The accumulated opposing electrostatic charges resultin an attractive electrostatic force that electrostatically holds thesubstrate 55 to the chuck 100.

Alternatively, the embedded electrode 110 can also comprise bipolarelectrodes 110 a, 110 b, as shown in FIGS. 4a and 4 b, that comprises atleast two substantially coplanar electrodes that generate substantiallyequivalent electrostatic clamping forces. A differential electricalvoltage is applied to each of the bipolar electrodes 110 a, 110 b tomaintain the electrodes at differential electric potential to induceelectrostatic charge in the substrate 55 and electrodes. The bipolarelectrodes 110 a, 110 b can comprise two opposing semicircularelectrodes 110 a, 110 b with an electrical isolation void therebetweenthat is covered by the dielectric member 115 as shown in FIG. 4a.Alternative electrode configurations 110 a, 110 b include inner andouter rings of electrodes, polyhedra patterned electrodes, or othersegmented electrode forms embedded in the dielectric member as shown inFIG. 4b.

In the arrangement shown in FIG. 3b, the electrode comprises anelectrically conductive plate 110 that is covered by a dielectric member115 comprising a layer or coating of dielectric material. The metalplate electrode 110 is shaped and sized to correspond to the shape andsize of the substrate 55 to maximize heat transfer and provide a largeelectrostatic holding surface for the chuck. For example, if thesubstrate 55 is disk shaped, a right cylindrically shaped plate ispreferred. Typically, the metal plate comprises an aluminum cylinderhaving a diameter of about 100 mm to 225 mm, and a thickness of about1.5 cm to 2 cm. By “electrode” 110 it is meant any of the aforementionedversions of the electrode, including both the embedded electrode layerand the metal plate electrode.

Particular aspects of the electrostatic chuck 100 of the presentinvention and illustrative methods of fabricating the chuck will now bedescribed. However, the present invention should not be limited to theillustrative examples and methods of fabrication described herein. Also,it should be understood that each of the individual components, layers,and structures described herein, for example, a semiconductingdielectric layer or electrical isolator structures, can be usedindependently of one another and for applications other thanelectrostatic chucking, as would be apparent to those of ordinary skill.

Electrical Isolator in Conduit

One feature of the electrostatic chuck 100 of the present inventionrelates to a plurality of heat transfer gas flow conduits 150 thatextend through one or more of the base 105, electrode 110, anddielectric member 115, as shown in FIGS. 2 through 4b. A gas supplychannel 155 supplies heat transfer gas to the conduits 150 via a gassupply tube 160 connected to a heat transfer gas source 165. A typicalgas flow conduit 150 comprises (1) an inlet 202 for receiving gas from agas channel 155, and (2) an outlet 204 for delivering the gas to a topsurface 170 of the dielectric member 115 on the chuck 100. The gas atthe top surface 170 of the chuck 100 regulates the temperature of thesubstrate 55 by transferring heat to or from the substrate 55. Thesubstrate 55 held on the chuck 100 covers and seals the edges of thedielectric member 115 to reduce leakage of heat transfer gas from theperipheral edge of the chuck 100. The dielectric member 115 can alsocomprise grooves 162 that are sized and distributed to hold heattransfer gas such that substantially the entire surface of the substrate55 is uniformly heated or cooled, such for example a pattern ofintersecting channels that cut through the dielectric member 115.Preferably, at least one conduit 150 terminates in a groove 162, andmore preferably, the conduits 150 terminate at one or more intersectionsof the grooves 162. Alternative groove patterns are described in, forexample, U.S. patent application Ser. No. 08/189,562, entitled“Electrostatic Chuck” by Shamouilian, et al., filed on Jan. 31, 1994,which is incorporated herein by reference in its entirety. The gas flowconduits 150, gas supply channel 155, and grooves 162 are formed byconventional techniques, such as drilling, boring, or milling.Typically, the heat transfer gas comprises helium or argon at a pressureof about 5 to about 30 Torr.

Referring to FIGS. 3a and 4 b, electrical isolators 200 are located inthe outlet 204 of the gas flow conduits 150 to reduce or prevent plasmaformation from the gas provided by the conduits 150. This version of theelectrostatic chuck is useful for holding substrates in high densityplasma environments, for example, where the electromagnetic energycoupled to the chamber is on the order of 5 to 25 watts per cm² atfrequencies of 1 to 20 MHZ. High density plasmas typically contain ahigher ion density of charged plasma species in thin plasma sheathsand/or plasma ions having ion energies in excess of 1,000 eV. Duringoperation of the chuck 100, the pressure of heat transfer gas below thesubstrate 55 counteracts and reduces the electrostatic clamping force onthe substrate 55 to form spaces or gaps at the interface. In highdensity plasma environments, the thin plasma sheath formed above thesubstrate 55 penetrates into these spaces forming an arc or glowdischarge at the back of the substrate 55 which can burn holes in thesubstrate 55 or chuck 100. The electrical isolator structures 200 reduceor altogether prevent formation of a plasma in the spaces adjacent tothe conduit 150 to significantly improve the lifetime of the chuck 100.

The electrical isolators 200 are fabricated from any dielectricmaterial, including ceramics and thermoplastic or thermoset polymers.Suitable polymers include polyimide, polyketone, polyetherketone,polysulfone, polycarbonate, polystyrene, nylon, polyvinylchloride,polypropylene, polyethersulfone, polyethylene terephthalate,fluoroethylene propylene copolymers, and silicone. Engineeringthermoplastics and thermoset resins loaded with about 35% to about 45%by volume glass or mineral fillers can be injection molded to form theelectrical isolator 200. Suitable ceramic materials include Al₂O₃, AlN,SiO₂, Si₃N₄; of which aluminum oxide, aluminum nitride, silicon nitride,and mixtures thereof, are preferred. More preferably, the dielectricmaterial comprises aluminum oxides which provides a degree of chemicallycompatibility with the aluminum of the electrode and base or a mixtureof aluminum oxides and silicon oxides, as described below. Thedielectric breakdown strength of the dielectric material is preferablyfrom about 4 to 40 volts/micron, and the electrical resistance ispreferably from about 10¹¹ to 10²⁰ Ωcm.

Preferably, the electrical isolator 200 comprises a plasma-deactivatingmaterial that is capable of deactivating, and consequently altogetherpreventing formation of a plasma adjacent to the gas conduits 150 belowthe substrate 55. The plasma-deactivating material comprises a porous,high surface area material lining the internal surfaces of the conduit150 that prevents plasma formation by limiting the kinetic energy and/ordissipating the electrical charge of ionized gaseous species. Althoughthe plasma deactivation mechanism is not precisely known, it is believedthat the high surface area provides active recombination sites thatstrip the electrical charge from plasma species incident on the surface.Also, tortuous small diameter pores in the plasma deactivating materialcontrol the kinetic energy of charged plasma species in the pores byproviding a small mean free path that limits acceleration, and resultantavalanche breakdown of the charged species, that is necessary to ignitea plasma. The small mean free path also results in fewer energytransferring collisions between charged gas species which furtherreduces plasma formation. In this manner, the porous and/or high surfacearea plasma-deactivating material prevents formation of a plasma in theregions below the substrate that are adjacent to the conduits 150.

The electrical isolators 200 preferably comprise continuous passagestherethrough that have small linear dimensions (i.e., diameter orlength) which prevent avalanche breakdown and plasma formation in theholes. Preferably, the diameter of the conduits is less than aboutdeactivating deactivating 0.5 mm, and more preferably less than about0.25 mm. At these dimensions, the operating pressure and power of thechamber 50 are too low to permit ionization of the heat transfer gas,thereby preventing formation of a plasma in the regions adjacent to theoutlets of the gas flow conduits 50 and electrically isolating thesurrounding electrode 110. The shape and distribution of the pores,volume percent porosity, pore size and distribution, and surface area ofthe plasma deactivating material all affect its plasma deactivatingproperties. Preferably, the plasma deactivating material comprises smalldiameter, randomly oriented, tortuous pores which, in conjunction withthe spaces between the separated grains, form continuous pathways orpore passageways having small diameters extending through the material.The randomly orientated pores are desirable to produce tortuouspassageways that avoid straight line pathways while providing continuouspassageways that allow heat transfer gas to flow therethrough. Thediameters of these pathways are typically of the same order of magnitudeas the ceramic particles used to form the porous material. The tortuouspathways increase the number of effective collisions between the chargedgaseous species and between the charged species and the pore wallsurfaces. Preferably, the porous material comprises pore passagewaysthat are typically sized from about 250 to about 375 μm in length, andhaving diameters ranging from about 1 to about 100 μm. Preferably, thevolume percent porosity of the plasma deactivating material is fromabout 10 to about 60 volume %, and more preferably from about 30 toabout 40 volume %. Most preferably, the plasma-deactivating materialtypically comprises a surface area per gram from about 20 cm²/g to about300 cm²/g.

The plasma-deactivating material can be formed in the conduit 150 usingconventional ceramic fabrication, thermal spraying. In one preferredembodiment, the plasma-deactivating material comprises a mixture ofaluminum oxides and silicon oxides. The aluminum oxide grains are heldtogether with intermixed silicon oxide glassy phase, and the resultantstructure comprises continuous pathways that are formed between theceramic grains and through its pores. The porous material can be formedby mixing the desired composition of alumina and silica, pouring theformulation in a mold shaped as the insert, and sintering the mixture at1400° C. to melt the silica glass around the alumina. The resultantstructure has a high porosity of about 5 to 50%, and tortuous poreshaving diameters typically ranging from 1 to about 25 microns.

In another method of fabrication, a flame spraying method is used toform the plasma-deactivating material. In this method, a hightemperature flame of a combustible mixture of gases, for example,acetylene and oxygen, is formed and a ceramic powder formulationcorresponding to the desired composition of the plasma deactivatingmaterial is sprayed through the hot flame. The flame spraying methodprovides a relatively low heat or kinetic energy input to the sprayedceramic particles, allowing them to move relatively slowly and cool offduring travel to the incident surface. The cooling and low kineticenergy impact on the conduit walls results in solidifiedplasm-deactivating material that comprises spherical ceramic particleswhich retain their shape and have extensive tortuous pathways betweenthe particles and have high surface areas.

Electrical Isolator Structures

The electrical isolator 200 in the gas flow conduit 150 can have manydifferent shapes and forms. In one embodiment that is easy to fabricate,the gas supply channel 155 with gas flow conduits 150 is machined in anannular metal ring 180 that is inserted in, and forms a portion of theelectrode 110, as illustrated in FIGS. 5a to 5 d. Referring to FIG. 5a,the annular ring 180 comprises a gas supply channel 155 machined in itsunderside in close proximity to its upper surface with a thin metallayer 185 therebetween. Conduits 150 are machined through the metallayer 185 in an annular configuration. The inlets 202 of the conduits150 are bored through the thin layer of metal 185 prior to theapplication of the overlying dielectric member 115 (not shown), or theconduits can be formed after the application of dielectric member bysimultaneously boring outlet holes 204 through the dielectric member 115and thin metallic layer 185. The annular ring 180 is sized to fit alongthe periphery of the electrostatic chuck 100, and is sealed at edges andsurfaces 190 adjacent to the central portion of the electrode 110 toreduce leakage of heat transfer gas. Preferably, as shown in FIG. 5b,the annular ring 180 and electrode 110 form a first annular gas flowchannel 155 a and an overlying and concentric second annular channel 155b having a larger width. The annular ring 180, including a plurality ofpredrilled conduits 150 spaced apart around the length of the annularring, is fitted into this combination of channels. The dielectric member115 (not shown) is applied over the surface of the ring 180 andprocessed to the desired thickness. Thereafter, an opening is drilledthrough the dielectric member 115 to connect to the conduit 150 to allowheat transfer gas to flow from channel 155 to the surface of theelectrostatic chuck.

In the version shown in FIG. 5b, the electrical isolator 200 a in thegas flow conduit 150 comprises a plurality of dielectric coatings 205,210 covering the sidewalls of the conduit. The dielectric coatings 205,210 can be deposited directly on sidewalls of the conduits formed in aannular ring 180 (as shown) or can be deposited on top of another“sidewall” dielectric coating that is initially deposited on thesidewalls of the conduit 150. For example, the first or inner sidewalldielectric coating 210 can comprise a highly electrically insulativelayer, and the outer coating 205 can comprise a coating of porous plasmadeactivating material.

FIG. 5c illustrates another embodiment in which the electrical isolatorcomprises a preformed dielectric insert 200 b inserted in the conduit150 and having at least one continuous hole or passageway 206 thatallows heat transfer or other gas to flow through the conduit 150. Thedimensions of the hole are selected to reduce plasma formation, andpreferably comprise a diameter equal to or less than about 0.4 mm. Thepreformed dielectric insert 200 b can be fabricated from electricalinsulator or dielectric material, plasma-deactivating material, ormixtures thereof. In general, the dielectric inserts 200 b arefabricated by positioning the insert into the conduit 150 drilled in anannular ring 180 with an apex of the insert extending from the electrode110. A layer of dielectric (not shown) is formed over the surface 208 ofthe annular ring 180 and electrode 110 and processed to the desiredthickness to expose the hole 206 of the insert 200 b. Thereafter, theapex is removed, for example, by grinding or ablating; or a dielectricmember 115 is formed around the apex to hold the dielectric insert 200 bin position. Dielectric insert 200 b electrical isolates the annularring 180 from process plasma which may penetrate the outlet of gas flowconduit 150 and reduces arcing between the substrate 55 supported uponthe surface of the electrostatic chuck 100 and the electricallyconductive annular ring 180.

FIG. 5d illustrates yet another embodiment of the present inventionwhere the electrical isolator comprises a plug 200 c of dielectricmaterial that substantially fills up the outlet of the gas flow conduit150. The plug 200 c comprises continuous pathways such as interconnectedpore passageways, microcracks, and separated grain boundary regions thatextend through the entire plug. Suitable plugs 200 c have porositiesranging from about 10 to about 60 volume %. In this embodiment, anoverlying dielectric member 115 covers the plug 200 c to hold the plugin place, and an opening is drilled through the dielectric member andstopped on the top surface of the porous plug 200 c. The continuous porepathways formed by the intersection of one or more pores, microcracks,and separated grain boundary regions in the porous plug 200 c allow heattransfer gas to flow therethrough, while reducing or preventing limitingplasma formation in the conduit 150.

Another version of the electrical isolator, as shown in FIG. 6,comprises a cylindrical dielectric insert 300 having a boss 301 aroundits circumference and a vertically extending cavity 308 extending fromthe bottom and having a closed off apex 306. The dielectric insert 300is conically shaped with tapering sides 314 at an angle of about 26°.The central portion is cylindrical with a diameter of about 1.5 mm (60mils), and the entire insert has a diameter of about 3.2 mm (127 mils).A socket hole 313 is bored in the electrode 110 to connect to theunderlying gas supply channel 155 in the electrode 110. Dielectricinsert 300 is fitted into the socket hole 313 with the bottom of itsboss 301 resting on the side portions of socket hole 313, leaving aclearance between the bottom of dielectric insert 300 and the gas supplychannel 155. Heat transfer gas flows from the gas supply channel 155into the vertically extending cavity 308 formed within dielectric insert300. After the dielectric insert 300 is fit into socket hole 313 ofelectrode 110, a dielectric member 302 is formed over the surfaces ofboth the dielectric insert 300 and electrode 110. Thereafter, thedielectric member 302 is ground back to line 304 which is below theclosed end of the cavity 308 of the insert 300, to expose the cavity 308at its apex 306 allowing heat transfer gas to flow therethrough.Preferably, a plurality of dielectric inserts 300 are inserted intorespective socket holes 313 spaced apart along the electrode 110, orinto socket holes formed in the annular ring 180 which is thereafterjoined to the electrode 110.

FIG. 7 shows another embodiment of the electrical isolator comprising atubular sleeve 320 shaped as a right circular cylinder with an axialopening 328 therethrough. The axial opening 328 passes through theentire sleeve 320 (or has an upper closed end, not shown). The tubularsleeve 320 is inserted in corresponding socket holes 334 in theelectrode 110 that connects to the underlying gas supply channel 155 ofthe chuck 100. A second socket hole 335 is drilled partially throughelectrode 110 to form an annular ledge 336 at the bottom of the sockethole 335 that supports the tubular sleeve 320. Optionally, a tubularsleeve 320 is held in the electrode 110 by an annular weld or brazedjoint 326 extending around the sleeve 320 at the top of the electrode110 or by an interference fit. After the tubular sleeve 320 is fittedinto socket hole 335, a dielectric member 322 is formed over the surfaceof insert sleeve 320, and thereafter ground back to line 324 to exposethe opening 332 of the sleeve 320. Instead of welding sleeve 320 inplace, layer 322 can be processed so that it leaves dielectric insert320 unexposed. Openings 332 are then drilled through semiconductingdielectric member 322 to connect with opening 328 in dielectric insertsleeve 320. Preferably, a plurality of such tubular sleeves 320 arepositioned around the electrode 110.

FIGS. 8a to 8 f show additional embodiments of the electrical isolators200 of the present invention. The overlying dielectric member 115 whichforms the upper surface of the electrostatic chuck 100 is not shown sothat the underlying structures can be shown with more clarity. Thedielectric insert 510 illustrated in FIG. 8a comprises a plurality ofopenings 516 leading to gas flow channel 155. Dielectric insert 510 isshaped to fit into annular ring 180 and comprises a dome-shaped uppersurface that, after application of an overlying dielectric member (notshown), can be ground or ablated to expose the openings 516 of thedielectric insert 510 while leaving a portion of the upper surface ofthe electrode 110 and the insert covered by the overlying dielectricmember.

The electrical isolator of FIG. 8b also comprises a dielectric insert520 that uses an overlying dielectric layer (not shown) to hold it inplace. The overlying dielectric layer (which serves as the dielectricmember 115) is applied over the surface of insert 520, annular ring 180,and electrode 110; and thereafter, ground or ablated to the desiredthickness. The conduits through the overlying dielectric layer anddielectric insert 520 are drilled through the overlying dielectric layerand insert 520 to connect to gas flow channel 155. FIG. 8c shows typicalhole patterns which can be drilled through the dielectric inserts 510,520 of FIGS. 8a and 8 b, respectively. Alternatively, the dielectricinserts 510, 520 can be fabricated from porous material without drillingholes therethrough, allowing the continuous pores and passageways of theinsert to allow heat transfer gas to flow therethrough.

In the embodiment shown in FIG. 8c, the conduits or grooves are formedin the electrical isolator 200 by laser micro-machining, a grindingwheel, or diamond/cubic boron nitride drilling. A preferred laser is anexcimer UV laser having a short wavelength and high energy that isoperated at a relatively low power level to reduce redeposition ofdrilled aluminum particles onto the walls of the openings and onto thedielectric member. Such aluminum contamination can cause arcing of thedielectric member 115. The number of outlet openings 204 for the conduitdepends on the heat transfer load and the gas flow rate required tohandle this load. For an electrostatic chuck 100 used with an 200 mm (8inch) silicon wafer, a suitable number of outlets 204 or openings forthe gas flow conduits range from about 12 to about 24, and the openingsare positioned in a ring-shaped configuration around the perimeter ofthe electrostatic chuck 100. Preferably, the diameters of the outlets204 are less than or equal to about 0.20 mm, and more preferably about0.175 mm.

Another series of dielectric insert designs, shown in FIGS. 8d through 8f, are positioned in the annular ring 180 fitted in an electrode 110having two annular trenches 602, 604 therein. In FIG. 8d, the dielectricinsert 610 comprises a tubular non-porous dielectric sleeve 616surrounding a porous dielectric insert 618. The dome-shaped upperportion of dielectric insert 610 allows the dielectric member 115 (notshown) to hold it in place. The overlying dielectric member 115 isground or ablated to expose porous dielectric insert 618, as shown inthe top view of FIG. 8e. This allows heat transfer gas to flow throughchannel 155 and porous dielectric insert 618 to the surface of thedielectric member. The non-porous dielectric sleeve 616 is shaped toform a small angle with the adjacent surface 612 of the annular ring180, allowing deposition of a contiguous coating without voids orcavities at the interface of the sleeve 616 and ring 180. The uppersurface of dielectric insert 616 is roughened to provide a strong bondwith the dielectric member 115. Preferably, dielectric sleeve 616 hasgreater tensile strength and modulus than the insert 618 to provide amore reliable joint between sleeve 616 and annular ring 180. This alsoreduces formation of voids between dielectric sleeve 616 and ring 180which can cause flaws in the overlying dielectric coating (not shown).FIG. 8f illustrates another dielectric insert 620 that entirelycomprises a porous dielectric material, such as the plasma-deactivatingmaterial having continuous pore passageways therein. The porosity andpore size distribution of the porous material is selected to reduceformation of plasma in and adjacent to the dielectric insert 620.

FIG. 9a shows yet another preferred configuration of a dielectric insert630 comprising a dielectric sleeve 636 and a dielectric center plug 638.An annular ring shaped opening 640 is between sleeve 636 and center plug638. Center plug 638 is held in place by an adhesive or ceramic bondingmaterial such as fusible glass ceramic 642, which anchors plug 638 tosleeve 636. By adjusting the size of dielectric center plug 638, the gasflow rate through dielectric insert 630 is adjusted. Again, an overlyingdielectric member 115 (not shown) is applied over the surfaces of theelectrode 110, annular ring 180, and dielectric insert 630. Subsequentlythe overlying dielectric member 115 is processed to expose the opening640 in dielectric insert 630 while leaving at least a portion of sleeve636 entrapped below the overlying dielectric member.

FIG. 9b shows a preformed electrical isolator 200 comprising a porousplug 820 in a polymer sleeve 832, the sleeve sized to hold the porousplug 820 in the conduit 150 in the dielectric member 115 or electrode110. Preferably, the sleeve 832 is made of a ductile, lubricative, andslippery surfaced polymeric material, such as Teflon® (trademark ofDuPont Company), or a silicone containing material. Because of itsductility and lubricative surface, the sleeve 832 facilitates insertionof the hard, brittle, and fracture-prone ceramic porous plug 820 intothe conduits 150 of the chuck. Also, the ductile and flexible polymerconforms its shape to fit snugly into the conduit, to eliminate the needfor machining the conduit and/or the porous plug to precise tolerances.In the fabrication process, the porous plug 820 is first press fittedinto the polymer sleeve 832, and the assembled electrical isolator 200is then press fitted into the outlet 204 of the conduit 150. Thepreformed insert in the sleeve 832 defines at least one continuouspassageway that allows gas to flow through the insert. While the ceramicinsert can be fabricated from aluminum oxide, aluminum nitride, silicondioxide, zirconium oxide, silicon carbide, silicon nitride, or mixturesthereof; of which aluminum oxide, aluminum nitride, or silicon nitride,are preferred.

In the embodiment shown in FIG. 9c, the electrical isolator 200comprises an outwardly extending spacer 835 that is sized to hold aninsert 830 in conduits 840, 850. Preferably, the spacer 835 is made of aceramic or plastic material, such as Teflon® (trademark of DuPontCompany tetrafluoroethylene polymer). The spacer 835 has a top tubularportion 860 and a bottom tubular portion 865 separated by a centralledge 870 having a cross-sectional area greater than the inner diameterof conduits 840, 850. The spacer 835 aligns and holds in place thetubular insert 830 during assembly of the chuck, and prevents ingress ofbonding material 855, such as molten solder, for example indium, intothe conduits 840, 850 during bonding of the chuck 100 to a base 105.Prior to joining the chuck 100 to the base 105 the top tubular portion860 is inserted into conduit 840 on the lower surface of the chuck andthe bottom tubular portion 865 is then aligned with and inserted intoconduit 850 in the base. The base/chuck assembly is placed into a mold,which is then evacuated by a vacuum pump and into which molten solder isinjected. The thickness of the central ledge 870 of a plurality ofspacers 835 interposed between the chuck 100 and the base 105 hold thechuck at a predetermined distance from the metal base to provides auniform bond line of predetermined thickness. A uniform bond lineprovides uniform thermal resistance which in turn promotes good heattransfer between the base 105 and the chuck 100. This is particularlyadvantageous in the embodiment in which the base 105 advantageouslycomprises heat transfer fluid channels 90 that are used to circulateheat transfer fluid to heat or cool the chuck 100 to regulate thetemperature of the substrate 55. As shown in FIG. 2, the base 105comprises channels 90 through which heat transfer fluid can becirculated by fluid circulator 88 to heat or cool the chuck 100 asneeded to maintain substrate temperature.

Yet another embodiment of a composite dielectric insert is shown in FIG.10a. In this embodiment, the dielectric insert 650 comprises a porousdielectric material shaped in the form of an inverted T-shape structure,and having a boss 652 around its circumference, the boss comprising avertical cylinder 654 with a closed upper end 656 centered on a discportion 658. The vertical cylinder 654 of the boss 652 typically has adiameter of about 1 to about 3 mm and the disc portion 658 a diameter ofabout 3 to about 5 mm. A non-porous sleeve 660 is shaped to fit andsurround the vertical cylinder 654. The tapered upper surface of thenon-porous sleeve 660 is roughened to allow strong adherence to theoverlying dielectric member 115. To fabricate the chuck, a socket hole662 is bored in the electrode 110 to connect to the underlying gassupply channel 155 in the electrode 110. Dielectric insert 650 is fittedinto the socket hole 662 with the bottom of its boss 652 resting on thebottom portions of socket hole 662, exposing the relatively wide area ofthe disc 658 to allow heat transfer gas to ingress into the insert 650from the gas supply channel 155, and thereafter flow into the verticallyextending cylinder 654. After the insert 650 is fit into socket hole 662of electrode 110, a dielectric member 115 is formed over the surfaces ofthe sleeve 650, the tapered roughened surface of the sleeve 660, andadjacent surfaces of the electrode 110. Thereafter, the dielectricmember 115 is ground back to exposed the closed end of the cylinder 654,and the porous pathways therein allow heat transfer gas to flow through.

In the embodiment shown in FIG. 10b, the dielectric insert 670 comprisesa boss 672 having conically shaped tapering sides at 674 at an angle ofabout 26°. In this version, a non-porous sleeve 676 comprising a tubularshape with an inwardly extending cap 678 is shaped and sized to fit overthe dielectric insert 670. The upper surfaces 680 of the nonporoussleeve 676 are roughened to form a surface having a strong mechanicaladherence. Glass or ceramic cement can be used to bond the cap 678 ofthe nonporous insert onto the boss 672 of the porous insert. Thereafter,the composite insert is positioned in a corresponding hole 682 in theelectrode 110, and the dielectric member 115 is formed over the insertand thereafter ablated or ground to expose the surface of the porousinsert, as described above.

In the embodiment shown in FIG. 11, the electrical isolator 200comprises a dielectric material shaped in the form of a column or pin836 having an embedded electrical conductor lead 838 that iselectrically connected to the grounded base 105 of the chuck. The lead838 is electrically connected to the base that is typically maintainedat an electrical ground, to bring the ground potential applied to thebase closer to the substrate to suppress the formation of plasma andelectrical arcing in the conduit 150. Each gas supply channel 155 of thechuck contains a centrally positioned dielectric pin 836 having adiameter sized smaller than the conduit to provide an annular orcircumferential opening that allows gas to flow from the channel 155past the dielectric pin 836 and below the substrate. The dielectric pin836 is held in place in channel 155 by an adhesive or bonding material720 applied to the base of the pin.

FIGS. 12a through 12 f illustrate a preferred embodiment of the presentinvention which provides ease in fabrication. Referring to FIG. 12e, thefinal structure comprises an electrode 110 including at least one gassupply channel 155 which contains dielectric insert 718. Dielectricinsert 718 is sized to provide an annular opening 716 that allows gas toflow from the channel 155 and past the dielectric insert 718, as shownin FIG. 12f. The dielectric member 115 overlying electrode 110 alsoincludes at least one opening directly over channel 155, the openingsized to allow insertion of dielectric insert 718 with the annularopening 716 around the insert 718. Thus, heat transfer gas can flow fromchannel 155 to the surface of the dielectric member 115 via the annularopening 716. Dielectric insert 718 is held in place in channel 155 by anadhesive or bonding material 720. It is not critical that dielectricinsert 718 be centered in the opening 710 through the dielectric member115, as long as the heat transfer gas can flow through the annularopening 716.

Fabrication of this embodiment, is shown in FIGS. 12a through 12 f. FIG.12a shows a gas supply channel 155 formed in the electrode 110, and atleast one hole or opening 710 is drilled through the surface 706 of theelectrode 110 to connect with heat transfer gas flow channel 155, asshown in FIG. 12b. The diameter of opening 710 is generally, but not byway of limitation, about 2 mm (0.080 inches) or larger. Although thisdiameter is not critical, the tolerance of the selected diameter shouldbe held within about ±0.13 mm (±0.005 inches). As shown in FIG. 12c, aspace-holding masking pin 712 is then held in opening 710 and channel155 so that overlying dielectric member 115 can be formed withoutexcessive dielectric material entering into opening 710. This is thereason the tolerance of the diameter of opening 710 should be carefullycontrolled. Masking pin 712 is preferably constructed from a materialwhich does not adhere to the dielectric member 115, such as a Teflon®(trademark of DuPont Company) masking pin 712. Space-holding masking pin712 is generally 3 to 6 diameters high; being sufficiently tall to allowpulling out the pin 712 after forming the dielectric member 115, andsufficiently small to reduce shadowing of the dielectric member 115around masking pin 712.

The dielectric member 115 is typically applied to a thickness which isfrom about 250 to about 600 microns (10 to 20 mils) greater than thedesired final thickness; and after application of dielectric member 115and removal of masking pin 712, as shown in FIG. 12d, the dielectricmember 115 is ground to final thickness, and cleaned of grindingresidue. This provides a smooth, flush surface 722 to the dielectricmember 115, which is flat to at least 25 microns, i.e., all points onthe surface lie within two parallel planes spaced 25 microns apart.Annular opening 716 typically has a diameter of about 2 mm (0.08 inches)or more to permit removal of surface residue, such as the grindingresidue. This is an advantage over other embodiments of this inventionwhich have smaller diameter openings and are more difficult to clean.

A measured quantity of adhesive or bonding ceramic 720 is then depositedat the base of channel 155, directly beneath opening 710. The thicknessof adhesive layer 720 is sufficient to compensate in variations in thelength of dielectric pin 718 while maintaining the smoothness of thechuck surface across the dielectric member 115 and dielectric pin 718.Dielectric pins 718 are typically fabricated from ground ceramic, suchas alumina, and have a diameter ranging from about 0.76 mm to about0.102 mm (0.003 to 0.005 inches) less than the bore diameter of opening710. Typically, the dielectric pins 718 are cut at least ¼ mm (0.010inch) shorter than the bore depth through dielectric member 115 andelectrode 110 to the bottom 726 of channel 155. Dielectric pins 718 maybe cut as much as 1 mm (0.040 inch) undersized in length.

Dielectric pins 718 are inserted through opening 710 and into adhesive720 resting on the bottom 726 of channel 155. It is important that thepins 718 are positioned to provide a flush top surface 724, and this isaccomplished using the depth of penetration of pins 718 into thethickness of adhesive 720 to make up any differences in length of pins718. It is not critical that dielectric pins 718 be centered within thebore openings 716 and 710, and variation is allowable, as apparent fromFIG. 12f. The heat transfer gas flows out of the annular opening 716between dielectric pin 718 and electrode 110. In an alternative method,the dielectric pin is held in place by an opening machined into thebottom surface 726 into which dielectric pin 718 is interference fittedor staked.

For electrostatic chucks 100 used to hold 8-inch diameter semiconductorwafers, approximately 12 to 24 conduits having dielectric inserts 718are positioned in a ring around the periphery of the chuck 100. Thecircular opening 710 in electrode 110 (or annular ring 180) typicallyranges from about 1 to about 10 mm (0.040 to about 0.400 inches) indiameter, and the dielectric insert has an outer diameter ofapproximately 0.123 mm (0.005 inches) smaller than the diameter of thecavity. These dimensions are adjusted depending on the kind of heattransfer gas used, the pressure in the process chamber, and the desiredgas flow rate to the surface of the electrostatic chuck 100.

Where the electrical isolator 200 is in close contact with an opening inthe electrode 110 or annular ring 180, a close contact can be achievedusing an interference fit or press fit. During press fitting of thedielectric insert 200 b in the opening, a uniform pressure should beapplied to the surface of the dielectric insert to prevent fracture ofthe brittle insert using a tool designed to fit and apply even pressureto the surface of the dielectric insert during press fitting. Ingeneral, electrical isolators 200 comprising ceramic dielectric insertsshould be small in size, about 0.5 mm (0.020 inches) to about 10 mm(0.400 inches) in diameter, to avoid mechanical failure from compressiveloads applied as a result of temperature cycling during substrateprocessing. The incompatibility of the thermal coefficient of expansionbetween the ceramic dielectric and the electrode 110 of theelectrostatic chuck 100 creates these compressive loads duringtemperature cycles. The small size of the dielectric insert also makesit possible to compression fit the insert into the electrostatic chuck100 in an interference fit. Also, the insert should be tapered towardits bottom edge to permit easier insertion into the receiving cavity.Since alumina containing dielectric inserts have relatively hard andsharp edges, the insert can be pressed into the underlying aluminumcavity with sufficient pressure to cut into the aluminum and provide aclose press fit. A close press fit is also obtained by deforming theconductive material in contact with the dielectric insert (staking). Thedielectric insert can also be closely fitted using a machinedinterference fit of about at least about 0.025 mm (0.001 inch). Also, alarge interference fit between the insert and surrounding base increasesthe strength of the bond of the overlying dielectric coating applied onthe base and insert, reducing thermal expansion microcracking of theoverlying dielectric member, which can lead to penetration of highdensity plasmas, and rapid breakdown of the dielectric member overlyingthe insert and base.

Another structure suitable for forming the electrical isolator 200comprises a porous plug 800, the manufacture of which is shown in FIGS.13a to 13 d. The porous plug 800 has substantially continuous pores,and/or interconnected microcracks and pores that forms continuouspathways that allow heat transfer gas to flow through the plug 800,while simultaneously deactivating or limiting plasma formation in theconduit 150. Referring to FIG. 13a, a hole having a straight walledinlet 802 and a tapered outlet 804 is bored through the electrode 110 toform a gas flow conduit 150. Thereafter, an underlying dielectric layer806 is deposited on the sidewalls of the conduit 150, and the surface810 of the dielectric layer 806 at the outlet 804 is roughened, forexample by grit blasting, to form a rough serrated surface that providesstrong mechanical adherence of the porous plasma deactivating material,and of the dielectric member 115 overlying the conduit. Preferably, thedielectric layer is deposited by plasma spraying to provide roughsurfaces yielding better adhesion. A tapered conically shaped porousplug 800 is formed over the roughed surface to fill the outlet of theconduit 150, by for example, thermal spraying. Alternatively, as shownin FIG. 13d, one or more conduits 150 terminating in circular grooves805 are formed in the surface of the chuck 100, a layer of dielectricmaterial 806 is deposited in the groove 805 and roughened, and a porouscovering 803 is filled in the groove 805. Preferably, at least onegroove 805 is formed in the peripheral edge of the electrode 110 to coolthe peripheral edge of the substrate. This configuration has the furtheradvantage of facilitating manufacture by allowing the underlyingdielectric layer 806 and the porous covering 803 to be deposited byrotating the chuck 100 under the applicator nozzle of the sprayingapparatus. Preferably, plasma or flame spraying is used to form theporous plug structure 800 to obtain a high porosity plug. Thereafter,the overlying dielectric member 115 is deposited on the plug 800 to holdthe plug in place, as shown in FIG. 13b. Either an opening is drilledonly through the dielectric member 115 (not shown) and stopped on thetop surface of the porous plug 800; or the surface of the dielectricmember is ground or ablated until the apex 812 of the plug is exposed,as shown in FIG. 13c, allowing heat transfer gas to flow through theporous pathways in the plug.

In the embodiments shown in FIGS. 13a to 13 c, the tapered outlet 804comprises a nonvertical surface which allows firm adherence and uniformdeposition of a thermally sprayed dielectric member 115. It has beendiscovered that when a thermally sprayed coating is applied to aperpendicular surface, i.e., in the same plane as the spraying directionof the spraying process, the solidified spray has low adhesion on thevertical surfaces and forms loose grains near the corners and edges ofthe vertical surfaces resulting in spalling and flaking off of thedielectric member 115. Thus, preferably, the outlet 804 of the conduit150 has non-vertical surfaces that define a tapered region therebetween.The tapered region is also configured to reduce the penetration ofplasma into the conduits 150, the sloped non-vertical walls forming anapex at the surface of the chuck. The porous plug 800 is deposited inthe tapered region to substantially entirely fill the tapered region ofthe outlet. Typically, the outlet 804 has tapered sides that form anangle of about 26° with a vertical axis through the conduit, andcomprises a first smaller diameter of at least about 1 mm, and a secondlarge diameter of less than about 5 mm.

In yet another method of fabrication, the electrical isolators 200 areformed by filling the outlet 204 of the conduit 150 with porousmaterial. The outlet 204 of the conduit 150 forms an annular ring thatextends continuously along, and adjacent to, the circumferentialperimeter of the chuck, as shown in FIG. 13d, to provide heat transfergas below the entire perimeter of the substrate 55. Preferably, granulesof dielectric material mixed with organic binder are packed in theoutlet 204 of the conduit 150, and sintered to form granular materialbonded to the inner surfaces of the conduit 150 having convolutedpassageways and interconnected pores. Because the dimensions of theresultant interconnecting pores tend to be roughly equal to the size ofthe granules, it is also preferred to use ceramic granules having anaverage mean diameter of less than or equal to about 0.4 mm, and morepreferably less than or equal to 0.25 mm. Preferably, the granulesconsist of the same material as the dielectric member 115 to increasetheir adhesion to the inner surface of the gas conduits 155 and reducethermal stresses. Thereafter, a layer of ceramic material is depositedover the electrical isolator 200, and a gas flow or gas pressure ismaintained in the electrical isolator 200 during deposition of theoverlying dielectric layer to prevent plugging of pre-drilled holes orpores of the porous materials. After the dielectric member 115 is formedon the surface of the chuck 100, a thickness of about 200 to 250 μm ofthe top surface of the dielectric member is ground or ablated to exposethe underlying electrical isolator 200. The grinding process isperformed using a diamond grit-coated grinding wheel that is registeredaccurately relative to the chuck 100 to grind-off the correct thicknessof the dielectric layer, and deionized water grinding fluid is used toreduce contamination.

Another embodiment of the porous plug configuration 820 is shown in FIG.14. In this version, a hole having a straight walled inlet 822 and atapered outlet 824 having a continuously varying multi-radius sidewalls,is bored through an annular ring 180 to form the gas flow conduit. Theannular ring is mounted in a cavity in the electrode 110 so that thering 180 rests upon ledges 826 in the base. Thereafter, an underlyingdielectric member 828 is deposited on the outlet 824 of the conduit andadjacent surfaces of the electrode 110. A tapered conically shapedporous plug 800 is formed over an underlying dielectric member 828 tosubstantially fill the outlet 824 by a suitable deposition method, suchas for example thermal spraying, and more preferably by plasma or flamespraying. Thereafter, an overlying dielectric member 115 is deposited onthe plug 800 to hold the plug in place. Either an opening is drilledonly through the dielectric member 115 (not shown) and stopped on thetop surface of the porous plug 820 without drilling through the plug; orthe surface of the dielectric member is ground or ablated until the apexof the plug is exposed (not shown) allowing heat transfer gas to flowthrough the porous pathways in the plug.

Semiconducting Dielectric Member

In another aspect, the present invention is directed to an electrostaticchuck 100 comprising one or more electrodes 110 covered by, and morepreferably embedded in, a dielectric member having semiconductingproperties that provides fast charging and discharging response time andrapid chucking and dechucking of substrates 55 held on the chuck 100.The semiconducting dielectric member 115 can be used in conjunction withthe electrical isolators 200 or separately without using the electricalisolators 200. The dielectric member 115 comprises a unitary body ofsemiconducting dielectric material covering or enclosing the electrode110 therein, as shown in FIGS. 2 and 4b; or one or more layers ofsemiconducting dielectric material covering an electrically conductiveelectrode 110 that serves as the electrode 110, as shown in FIG. 3a. Inboth versions, the semiconducting dielectric member 115 comprises a topsurface 170 configured to support a substrate. Upon application of avoltage to the electrode 110, the semiconducting properties of thedielectric member 115 allow rapid accumulation of electrostatic chargein the dielectric member, particularly at the interface between thedielectric member and the substrate 55. For electrostatic charge toaccumulate in the dielectric member 115 the semiconducting material hasto be sufficiently leaky to allow a small leakage current to flow fromthe electrode 110 through the dielectric member 115. If the leakagecurrent is too small, chucking speed is slow, and substrate processingthroughput is reduced. Conversely, an excessively high leakage currentcan damage the active devices formed on the substrate 55.

The amperage of the leakage current that can be tolerated in the chuck100 also depends upon the voltage applied to the electrode 110. Thehigher the applied voltage, the larger the leakage current that can betolerated without completely losing the electrostatic clamping forcefrom excessive current leakage through the semiconducting dielectricmember 115. However, the maximum operating voltages that can be used toelectrostatically hold semiconductor substrates are limited to about2000 volts, and if exceeded, can cause charge-up damage of the activedevices in the substrate 55. Thus, the leakage current provided by thesemiconducting material should be sufficiently low to retainelectrostatic charge in the dielectric member 115, during operation thechuck at voltage levels of about 100 to about 1500 volts. It has beendiscovered that optimal leakage currents from the dielectric member 115,that provide quick charging response times, without damaging the deviceson the substrate, are at least about 0.001 mAmps/cm², and morepreferably from about 0.002 mAmp/cm² to about 0.004 mAmp/cm². A suitableleakage current is achieved by controlling the resistivity of thesemiconducting dielectric member 115. Thus, preferably, the resistivityof the semiconducting dielectric member 115 is sufficiently low to allowconductance of a low amperage leakage current that provides a quickcharging time of less than about 3 seconds, and more preferably lessthan about 1 second. The semiconducting dielectric member 115 also has aresistivity sufficiently low to provide rapid dissipation of accumulatedelectrostatic charge when the voltage applied to the electrode 110 isturned off. Preferably, the resistivity of the semiconducting dielectricmember 115 is sufficiently low to allow accumulated electrostatic chargeto substantially entirely discharge or dissipate in less than about 1second, and more preferably in less than about 0.5 second. Conventionaldielectric members typically have dechucking times of 5 to 10 seconds,which is about five to ten times longer than that provided bysemiconducting dielectric member of the present invention.

While a low resistance semiconducting dielectric member 115 is desirablefor rapid chucking and dechucking, a chuck having an excessively lowresistance dielectric member will allow excessive charge to leak out.The resistance of the semiconducting dielectric member 115 needs to besufficiently high to maintain a supply of electrostatic charge at theinterface of the chuck 100 and substrate 55, even though a portion ofthe electrostatic charge leaks or dissipates through the member 115. Anyleakage current allows electrostatic charge to continually dissipatefrom the dielectric member 115. Thus, electrostatic charge mustaccumulate at the dielectric/substrate interface at a rate equal to orgreater than the rate of charge dissipation to provide an equilibriummode in which a supply of accumulated electrostatic charge is maintainedat the dielectric/substrate interface.

In a preferred version, the semiconducting dielectric member 115comprises a resistance in a preferred range of resistivity Δρ thatprovides such a combination of opposing properties. The resistivityrange Δρ of the semiconducting dielectric member 115 is defined by (i) afirst lower resistivity ρ_(L) that is sufficiently low to allow aleakage current to flow from the electrode when the operating voltage isapplied to the electrode to form accumulated electrostatic charge at theinterface of the substrate 55 and the semiconducting dielectric member115; and (ii) a second higher resistivity ρ_(H) that is sufficientlyhigh to maintain accumulated electrostatic charge at the interfaceduring operation of the chuck without use of excessively high operatingvoltages that damage the substrate. The optimal range Δρ of resistivityof the semiconducting dielectric member 115 is preferably from about5×10⁹ to about 8×10¹⁰ Ωcm, and more preferably from about 1×10¹⁰ toabout 5×10¹⁰ Ωcm. This range of resistivity is substantially lower thanconventional dielectric members which have resistivities exceeding1×10¹¹ Ωcm, and more often exceeding 1×10¹³ Ωcm.

The semiconducting dielectric member 115 having the described propertiescan be fabricated from ceramic materials, polymers, and mixturesthereof. Suitable ceramic materials include (i) oxides such as Al₂O₃,BeO, SiO₂, Ta₂O₅, ZrO₂, CaO, MgO, TiO₂, BaTiO₃, (ii) nitrides such asAlN, TiN, BN, Si₃N₄), (iii) borides such as ZrB₂, TiB₂, VB₂, W₂B₃, LaB₆,(iv) silicides such as MoSi₂, WSi_(x), TiSi_(x) or (v) silicon carbide.Preferably, the semiconducting dielectric member 115 having aresistivity in the preferred range of resistivities of Δρ comprises acomposition of aluminum oxide doped with (i) transition metals or metaloxides, such as for example, Ti, Cr, Mn, Co, Cu, TiO₂, Cr₂O₃, MnO₂, CoO,CuO, and mixtures thereof; (ii) alkaline earth metals or oxides, such asfor example, Ca, Mg, Sr, Ba, CaO, MgO, SrO, or BaO; or (iii) a combinedoxide formulation, such as for example, CaTiO₃, MgTiO₃, SrTiO₃, andBaTiO₃. The dopant material is added in a sufficient quantity to providesemiconducting properties to the aluminum oxide dielectric material. Bysemiconducting it is meant a material having a conductivity in betweenthat of a metal and an insulator.

Preferably, the dielectric member 115 comprises a unitary body ofmultiple layers of semiconductor and/or insulating material enclosingthe electrodes, each layer typically having a thickness of from about 10μm to about 500 μm. The dielectric member 115 comprises a cover layerthat electrically isolates the substrate 55 from the electrode 110, anda support layer which supports the electrode and electrically isolatesthe electrode 110 from a conductive electrode 110. The material andthickness of the cover layer are selected to allow the DC voltageapplied to the electrode to electrostatically hold the substrate bymeans of Coulombic or Johnsen-Rahbek electrostatic attractive forces.The thickness of the layer covering the electrode is typically fromabout 100 μm to about 300 μm. Preferably, material of the cover layercomprises a dielectric constant of at least about 2. Additionally, aprotective coating (not shown) can be applied on the exposed surface ofthe dielectric member to protect the semiconductor layer from erosiveprocessing environments.

A preferred composition of the semiconducting dielectric membercomprises aluminum oxide doped with titanium oxide in a weight percentcontent of at least about 8 wt %, and preferably at least about 12 wt %.Whereas, pure aluminum oxide has a resistivity of 10¹⁴ Ωcm and acharacteristic charging response time of about 10³ seconds; the highlydoped aluminum oxide has a resistivity typically ranging from about5×10⁹ Ωcm to about 8×10¹⁰ cm. It is believed that the low resistivityresults from titanium-metal rich grains or grain boundaries that areformed in the aluminum oxide material, titanium-metal rich regionscomprising Ti³⁺in solid solution in the aluminum oxide structure.However, the resistivity can also be dependent upon microstructuralfactors other than Ti³⁺formation, for example, formation of highlyconductive Al_(x)Ti_(y)O_(z) phases within the alumina grains or atgrain boundary regions. Formation of highly conductive titanium-metalrich alumina grains is particularly prevalent when the TiO₂—Al₂O₃mixture is exposed to an oxygen-deficient or reducing environment, suchas an inert gas environment during fabrication.

The semiconducting dielectric member 115 operates by Johnsen-Rahbekforces providing a higher electrostatic clamping force for relativelylow chuck voltages. The low chuck voltages reduce the potential fordamage to active regions in the substrate 55. Also, the lower chuckvoltages reduce the risk of plasma generation at thedielectric/substrate interface. The semiconductor dielectric issufficiently leaky that upon application of a voltage to the electrode,the semiconducting dielectric member allows rapid accumulation ofelectrostatic charge at the dielectric/substrate interface. Furthermore,the low resistance semiconducting layer 115 provides electrostaticcharge dissipation response times of less than about 1 second, and moretypically less than about 0.5 seconds, with little or no residual chargeor sticking forces. The extremely low charging and charge dissipationresponse time provides rapid chucking and dechucking with theelectrostatic holding force rising almost instantaneously with appliedvoltage, and decreasing almost instantaneously to zero when the appliedvoltage is turned off. Also, unlike conventional ceramic formulations,the resistivity of the highly doped alumina coatings did not appear tochange during use at temperatures ranging from −10° C. to 100° C. Thesenovel and unexpected advantages of the semiconducting dielectric member115 provide significant benefits for electrostatic chucks.

In yet another aspect of the invention, as shown in FIG. 15, a compositedielectric member 115 comprising a first dielectric material 172 havingfirst electrical properties; and a second dielectric material 174 havingsecond electrical properties, is used to cover the electrode 110 (whichis illustrated as a base 105 that serves as the electrode, but alsoincludes the embedded electrode version). In a preferred configuration,the first dielectric material 172 is disposed over a central portion ofthe electrode 110 (which is substantially entirely covered by thesubstrate 55 during operation of the chuck 100); and the seconddielectric material 174 is disposed over a peripheral portion of theelectrode 110 and comprises an annular rim extending around the firstdielectric member. This configuration allows tailoring of the propertiesof the composite dielectric layers across the radial surface of thechuck. This is desirable to provide different electrical properties atthe edge of the chuck which is closer to the plasma sheath than thecenter which is covered by the substrate.

The properties of the first and second dielectric members 172, 174 aretailored to achieve different electrical properties at differentportions of the chuck 100. For example, the first dielectric member 172can comprise a semiconducting material as described above. Duringoperation of the chuck 100, the first dielectric member is substantiallyentirely covered by the substrate which serves as a dielectric materialthat electrically insulates the semiconducting layer and reducesshorting between the semiconducting layer and the plasma. In thisversion, the second dielectric member 174 comprises an insulator thathas a higher resistivity than the semiconducting dielectric member toprevent plasma discharge at the exposed peripheral portions of thechuck. The resistivity of the insulating second dielectric member 174 issufficiently high to prevent electrical discharge or arcing between thesurrounding plasma environment and the peripheral portions of the chuckelectrode. Preferably, the second dielectric member 174 has a resistanceof at least about 1×10¹¹ Ωcm, and more preferably from about 10¹³ Ωcm toabout 1×10²⁰ Ωcm. This configuration prevent shorting and arcing betweenthe leaky semiconducting dielectric member and the plasma and theresultant pinholes in the dielectric member that cause failure of thechuck. In another example, the composite dielectric coating 115 cancomprise a first dielectric member 172 having a first dielectricbreakdown strength, and a second dielectric member 174 having a seconddielectric breakdown strength. Preferably, the second dielectricbreakdown strength is higher than the first dielectric breakdownstrength to prevent plasma discharge or electrostatic chargeneutralization at the peripheral edge of the chuck.

The composite dielectric member 115 can also be made from multiplevertically stacked layers. For example, a multilayer compositedielectric member 115 can comprise (i) an Al₂O₃—TiO₂ layer providingsemiconducting electrical properties; and (ii) a more insulative secondlayer, such as polyimide, Teflon®, SiO₂, or ZrO₂. For example, themultilayer structure can be tailored to provide increased electrostaticcharge retention at the top surface 170 of the chuck, and/or fasterelectrostatic charge accumulation and dissipation response times throughthe body of the dielectric member. This can be accomplished by forming athin second dielectric member having a high resistivity over a firstdielectric member having a lower resistivity. Because the electrostaticforce is largely attributable to the charge concentrated near thesurface of the dielectric member 115, such multilayer coatings, canprovide excellent surface charge retention characteristics, withoutaffecting charge dissipation from the underlying layer. The multipledielectric members preferably comprise a combination of semiconductingand insulator dielectric members.

The semiconducting or composite dielectric member 115 can be formed by avariety of conventional methods, as apparent to those skilled in theart, including for example, isostatic pressing, thermal spraying,sputtering, CVD, PVD, solution coating, or sintering a ceramic blockwith the electrode 110 embedded therein; as would be apparent to thoseskilled in the art. In the methods described below, the semiconductingdielectric member 115 is used to cover at least a portion of theelectrically conductive base that serves as the electrode 110, or isused to cover or entirely enclose an electrode 110 to form anelectrostatic member that can be supported by the base.

A preferred method of forming a unitary dielectric member 115 with anembedded electrode uses a pressure forming apparatus, such as anautoclave, platen press or isostatic press. Isostatic presses arepreferred because they apply a more uniform pressure on the dielectricmember and electrode assembly. Typical isostatic press comprise apressure resistant steel chamber having a diameter ranging from about 1to 10 feet. A pressurized fluid is used to apply pressure on anisostatic molding bag. A powdered precursor is prepared comprising asuitable ceramic compound as described above is mixed with an organicbinder selected to burn off during sintering. The precursor is placedalong with the electrode structure in the isostatic molding bag and thebag is inserted in the isostatic press. The fluid in the pressurechamber is pressurized to apply an isostatic pressure on the dielectricassembly. It is desirable to simultaneously remove air trapped in theisostatic molding bag using a vacuum pump to increase the cohesion ofthe powdered precursor. The unitary dielectric member/electrode assemblyis removed from the molding bag and sintered to form a unitarydielectric with the electrode embedded. The gas flow conduits 150 areformed in the dielectric member by conventional techniques, such asdrilling, boring, or milling. Preferably, at least some of the conduits150 terminate at the periphery of the chuck 100, to provide heattransfer gas to the peripheral edge of the substrate 55.

After deposition, the surface of the dielectric member 115 is fineground to obtain a highly flat surface to efficiently electrically andthermally couple the substrate 55 on the chuck 100. In a typically highdensity plasma, the driving point RF bias impedance presented by theplasma is very low. To achieve uniform ion flux energy to the substrate55 it is necessary to uniformly couple RF energy from the plasma throughthe substrate 55 to provide a constant plasma sheath voltage across thesurface of the substrate 55. Nonuniform plasma sheath voltages resultdifferent processing rates or attributes across the substrate surface.The uniformity of the plasma sheath voltage is a function of theimpedance/area of the plasma sheath, the substrate 55, the gap betweenthe substrate 55 and the chuck 100, and the chuck 100. A nonuniformimpedance or rough surface on the chuck 100 creates uneven impedancesbetween the chuck and the substrate, resulting in nonuniform plasmasheath voltage. Thus, it is desirable for the chuck 100 to have asubstantially flat and planar dielectric member 115 to provide uniformimpedance in the gap between the dielectric member 115 and thesubstrate. Besides providing strong electrical coupling, a flat andsmooth dielectric member also provides strongly thermally coupling andgood heat transfer properties from the substrate 55 to the chuck 100.Thus conventional diamond grinding wheels are used to grind thesemiconducting dielectric member 115 to a surface roughness of about0.007±0.001 mm, which is typically less than about 30 rms.

Alternatively, the dielectric member 115 can comprise a layer ofdielectric material formed directly on the electrode 110 or electrode110 using thermal spraying methods, such as for example, plasma glowdischarge spraying, flame spraying, electric wire melting, electric-arcmelting, and detonation gun techniques, as described below. Prior to useof the thermal spraying methods, the upper surface of the electrode 110or base 105 (which to avoid repetition are collectively referred toherein as electrode 110), that is typically made of a conductive metalsuch as aluminum or copper, is abraded by grit blasting to provide aroughened surface that enhances adhesion of the dielectric member 115.In the grit blasting process, the surface of the electrode 110 isblasted at a predetermined grit spray incidence angle. Furthermore, byrotating the base during blasting, microscopic grooves are formed whichundercut the aluminum surface to provide mechanical interlocking of adielectric member that is subsequently formed on the grooved andundercut surface. In this process, the electrode 110 is fixed to arotating turntable that rotates the electrode 110 around a centerline.The grit is blasted onto the surface of the electrode 110 using a nozzleoriented at an angle to the surface of the base. The nozzle travels fromthe outer edge to the center of the base at a variable speed to maintainthe depth and the pitch of the grit blasted grooves. Typically, the rateof nozzle travel increasing as the nozzle moves from the outer edgetoward the center. For example, an aluminum electrode 110 was fixed to aturntable which rotated at about 20 to 30 revolutions per minute (rpm),and the angle of incidence of the nozzle relative to surface of thealuminum electrode 110 was about 70°. A grit of particle size of about60 to 80 mesh, was grit blasted using a paint removal type nozzle, ontothe base. The height of the grit blasted grooves was about 0.025 mm(0.001 inch), and their pitch was about 0.073 mm (0.003 inch).

After preparation of the surface of the electrode 110, a coating ofsemiconducting material is formed on the electrode 110. Preferably, athermal spraying process is used to apply the selected ceramicformulation. For example, an alumina-titania composition is sintered toform a homogeneous frit, and ground to form a fine particle sizedceramic powder having an average particle size ranging from about 10 toabout 100 μm. The spraying process partially melts and energeticallyimpacts the ceramic powder onto the electrode 110. Typically, theelectrode 110 is maintained at a temperature of about 60° C. to about80° C., and the ceramic powder is thermally sprayed at an angle of about80° to 90° (nearly perpendicular) to the surface of the base. Thethermally sprayed coatings can bounce-off the surface, so it isimportant to apply the coating at a proper angle to the base to reducemicrocracking and provide dense layers. The high kinetic energy of themolten fine ceramic particles provide a dense, low porosity, dielectricmember having the desired semiconducting properties and low resistivity.The semiconducting dielectric member 115 should be sufficiently dense tocompletely electrically insulate the electrode 110 of the chuck 100. Alow or zero electrical resistance at any point in the semiconductingdielectric member 115 can result in an electrical short. Low electricalresistance can occur when the semiconducting dielectric member 115 isdamaged during spraying, i.e., by large macroscopic cracks; or if thedielectric coating is too porous and allows plasma to permeate throughthe pores and electrically short the dielectric member 115. Aftercooling, the peel strength of the thermally sprayed alumina/titania wastested using ASTM methods and found to have improved by about 20% overthat obtained using other coating methods.

Different thermal spray methods of forming the semiconducting layer 115will now be described. Referring to FIG. 16, a plasma glow dischargespraying process uses a plasma gun 240 consists of a cone-shaped cathode242 inside a cylindrical anode 244 which forms a nozzle. An ionizableinert gas, typically argon, argon/hydrogen, or argon/helium, is flowedthrough the plasma zone between the electrically biased anode andcathode where it is ionized to form a plasma. Ceramic powders injectedinto the plasma zone are accelerated and melted by the high temperatureplasma. Molten droplets are propelled onto the electrode 110, where theysolidify and accumulate to form a thick, well-bonded, and densesemiconducting dielectric member 115. The process has sufficient thermalenergy to completely melt high temperature ceramic materials, such asalumina and/or titania.

In the flame spraying method, a highly combustible mixture of acetyleneand oxygen is used to melt a sprayed ceramic powder sprayed through theflame. In this method, a high temperature flame is produced using acombustible mixture of gases, for example acetylene and oxygen, as shownin FIG. 17. A typical flame spraying gun 250 comprises a fuel supply 252and an oxygen supply 254. The oxygen enriched fuel mixture is ignited bya sparking means, such as a spark plug 256. The resultant high velocityignited gas melts the ceramic particles injected through the nozzle 258and the molten particles impinge on the electrode 110. The flamespraying method provides a relatively low heat or energy input to theceramic powder. The low kinetic energy ceramic particles travelrelatively slowly from the flame to the surface of the electrode 110allowing the particle to cool during travel. As a result of the cooling,and the relatively low kinetic energy impact on the electrode 110 thesolidified plasma-deactivating material comprises spherical ceramicparticles that retain their shape, providing pores and tortuous pathwaysbetween the particles that provide a high surface area.

Another method comprises a detonation gun technique (not shown). In thismethod, a rapidly expanding mixture of ignited gases imparts a highkinetic energy to powdered ceramic material that provides a densecoating on impact with the electrode 110. In the detonation gun, aseries of detonation explosion are used to provide extremely high energymolten ceramic particles that impact the electrode 110 to form a verydense ceramic material having novel electrical properties. The highvelocity detonation melts and expels the ceramic particles from a gunlike nozzle directed toward the electrode 110. Typically, the hotexpanded gases comprise a velocity of about 600 m/sec (2000 ft/sec) toabout 900 m/sec (3000 ft/sec), and a succession of such detonationsprovide the resultant coating thickness on the substrate.

Preferably, the dielectric member 115 is formed by an electric arcmelting method, as shown in FIGS. 18 and 19. A typical electric arcmelter comprises a circular ring-shaped cathode 262 with a hole 264therethrough, and a needle-shaped anode 266 centered within the cathode(as shown in FIG. 18) or adjacent to the cathode (not shown). The fineceramic powder from a source 268 is sprayed around the anode usingcarrier gas from a carrier gas supply 270, at a feeding rate of about 2to about 10 gm/min. The powdered ceramic material is transported by acarrier gas through the channels 272 on either side of the needle-shapedanode 266 and is directed through the opening 264 having a diameter ofabout 1 to 10 mm. An electric arc 274 is formed by applying a voltage Vsufficiently high to substantially entirely melt the ceramic powderbeing sprayed into the arc. The ceramic powder melts in the hightemperature electric arc 274 and highly energetically impinges on theelectrode 110. Also, important in the electric arc melting process isthe distance d between the ring-shaped cathode 262, the anode nozzle266, and the substrate 55, commonly referred to as the spray distance.The distance d between the arcing electrodes and the chuck electrode isselected so that the ceramic powder impinges on the chuck electrode in asubstantially molten state. In one version, the distance d may be fromabout 50 to 400 nm.

The carrier gas that is used to transport the ceramic powder can be aninert gas, a reducing gas, or an oxidizing gas. A reducing gas canincrease formation of non-stoichiometric transition metal compounds inthe alumina to reduce the resistivity of the ceramic while retaining itsmechanical properties. Also, oxidizing gas are generally undesirablebecause they cause excessive oxidation of the alumina resulting in highresistivity dielectric members 115. Preferably, the carrier gascomprises a non-reactive gas, such as an inert gas, for example, argon,helium, or xenon. Most preferably, argon gas is used to transport theceramic particles at a flow rate of about 20 to 100 l/min.

The ceramic powder sprayed into the electric arc 274 melts while passingthrough the highly energetic and extremely hot electric arc 274 to formmolten droplets that impinge on the electrode 110. The energized moltengrains impinge on the base and rapidly solidify due to conduction andconvection cooling at the incident surface. The in-flight convectioncooling of the molten droplets is minimized by the high kinetic energyimparted to the molten droplets by the electric arc. This restrictsgrain growth and improves homogeneity by reducing segregation ofimpurities. Although the mechanism is not understood, it was discoveredthat the electric arc melting process provided flattened ceramic grains(schematically illustrated in FIG. 19), small grain sizes, and grainboundary compositions that give rise to entirely different electricaland thermal properties, such as the controlled electrical resistivitydesired in the semiconducting layer. Of primary importance is thedroplet velocity and temperature, which are controlled by the ratio ofthe kinetic energy to heat input provided by the electric arc meltingprocess to the ceramic powder traveling through the arc. The highkinetic energy and heat input provided to the ceramic particles by theelectric arc melting process results in a high speed “splatting” ofmolten particles on the surface of the electrode 110 causing spreadingof the particles, rapid cooling from 500-600° C. to room temperature,and solidification in about 15-20 microseconds. This provides a densecoating with the required distribution of conductive titania species inthe alumina composition. The electric arc melting methods providedhighly dense Al₂O₃/TiO₂ compositions having resistivities of from 1 to5×10¹¹ Ω-cm. Scanning electron microscope (SEM) photomicrographs showeddense coatings with homogeneously dispersed porosity of less than about10%, and often less than about 5%.

The thermally sprayed ceramic coatings form submicron microcracks 276upon cooling and solidification that permit the dielectric member 115 toexpand or stretch to conform with the differential thermal expansionbetween the dielectric member 115, electrode 110, and/or electricalisolators 200, without forming large-sized cracks or delaminating fromthe underlying electrode 110. Large cracks allow plasma to enter throughthe microcracks 276 thereby damaging the electrode 110 and dielectricmember 115. However, small microcracking is desirable as long as thecracks are submicron sized, relatively uniformly distributed, and formedalong inhomogeneous grains and grain boundaries without propagatingthrough the entire thickness of the dielectric member 115. Suchcontrolled microcracking prevents delamination and cracking-off of thedielectric member 115 from the thermal expansion stresses at highprocess temperatures. For example, microcracking prevents aluminum oxidecontaining dielectric member 115 (which has a thermal expansion close tothat of pure alumina of about 4.3×10⁻⁶ in/in/° F.) from delaminating andseparating from the underlying aluminum electrode 110 (which has a muchhigher thermal expansion of about 13×10⁻⁶ in/in/° F.).

Although the present invention has been described in considerable detailwith regard to the preferred version thereof, other versions arepossible. For example, the semiconducting dielectric member 115 can beused in other applications, and can be fabricated from equivalentcompositions that provide quick chucking and dechucking response times.Also, the electrical isolator 200 can be fabricated in many other shapesand forms that are equivalent in function to the illustrative structuresherein. Therefore, the appended claims should not be limited to thedescription of the preferred versions contained herein.

What is claimed is:
 1. An electrostatic chuck comprising: an electrode;a semiconducting dielectric covering at least a portion of theelectrode, the semiconducting dielectric having an electricalresistivity of from about 5×10⁹ Ωcm to about 8×10¹⁰ Ωcm; and at leastone conduit extending through the electrode and an electrical isolatorin the conduit.
 2. An electrostatic chuck according to claim 1 whereinthe semiconducting dielectric comprises aluminum oxide, aluminumnitride, silicon dioxide, silicon carbide, silicon nitride, titaniumdioxide, zirconium oxide, or mixtures thereof.
 3. An electrostatic chuckaccording to claim 1 wherein the semiconducting dielectric comprises anelectrical resistivity of from about 1×10¹⁰ Ωcm to about 5×10¹⁰ Ωcm. 4.An electrostatic chuck according to claim 1 wherein the semiconductingdielectric comprises aluminum oxide.
 5. An electrostatic chuck accordingto claim 1 wherein the semiconducting dielectric comprises titaniumoxide.
 6. An electrostatic chuck according to claim 1 wherein thesemiconducting dielectric comprises aluminum oxide and at least about 8wt % titanium oxide.
 7. An electrostatic chuck according to claim 1wherein the electrical isolator is capable of reducing plasma formationin the conduit in a plasma environment.
 8. An electrostatic chuckaccording to claim 1 wherein the semiconducting dielectric comprises anelectrical resistivity sufficiently low to allow dissipation ofaccumulated electrostatic charge in less than about 1 second.
 9. Asubstrate process chamber comprising: a gas distributor adapted tointroduce process gas in the chamber; a semiconducting dielectriccovering an electrode, the semiconducting dielectric having a receivingsurface adapted to receive a substrate and the semiconducting dielectrichaving an electrical resistivity of from about 5×10⁹ Ωcm to about 8×10¹⁰Ωcm; at least one conduit extending through the electrode and anelectrical isolator in the conduit; and a plasma generator.
 10. Aprocess chamber according to claim 9 wherein the semiconductingdielectric comprises an electrical resistivity of from about 1×10¹⁰ Ωcmto about 5×10¹⁰ Ωcm.
 11. A process chamber according to claim 9 whereinthe semiconducting dielectric comprises aluminum oxide, aluminumnitride, silicon dioxide, silicon carbide, silicon nitride, titaniumdioxide, zirconium oxide, or mixtures thereof.
 12. A process chamberaccording to claim 9 wherein the semiconducting dielectric comprisesaluminum oxide.
 13. A process chamber according to claim 9 wherein thesemiconducting dielectric comprises titanium oxide.
 14. A processchamber according to claim 9 wherein the semiconducting dielectriccomprises aluminum oxide and at least about 8 wt % titanium oxide.
 15. Aprocess chamber according to claim 9 wherein the electrical isolator iscapable of reducing plasma formation in the conduit in a plasmaenvironment.
 16. A process chamber according to claim 9 furthercomprising a voltage supply adapted to supply a plasma generatingvoltage to the electrode.
 17. A process chamber according to claim 16wherein the voltage supply is adapted to supply a DC voltage to theelectrode to electrostatically hold the substrate.
 18. An electrostaticchuck comprising: an electrode; a semiconducting dielectric covering atleast a portion of the electrode, the semiconducting dielectriccomprising a surface to receive a substrate, and the semiconductingdielectric having a resistivity (i) sufficiently low to allow anelectrical charge applied to the electrode to leak from the electrodeand accumulate as electrostatic charge in the semiconducting dielectricand (ii) sufficiently high to retain the accumulated electrostaticcharge in the semiconducting dielectric during processing of thesubstrate, whereby the substrate may be electrostatically held to thesemiconducting dielectric; and at least one conduit extending throughthe electrode and an electrical isolator in the conduit.
 19. Anelectrostatic chuck according to claim 18 wherein the semiconductingdielectric comprises a resistivity sufficiently low to allow theaccumulated electrostatic charge to dissipate in less than about 1second upon termination of the electrical charge applied to theelectrode.
 20. An electrostatic chuck according to claim 18 wherein thesemiconducting dielectric comprises a resistivity of from about 5×10⁹Ωcm to about 8×10¹⁰ Ωcm.
 21. An electrostatic chuck according to claim18 wherein the semiconducting dielectric comprises a resistivity of fromabout 1×10¹⁰ Ωcm to about 5×10¹⁰ Ωcm.
 22. An electrostatic chuckaccording to claim 18 wherein the semiconducting dielectric comprisesaluminum oxide, aluminum nitride, silicon dioxide, silicon carbide,silicon nitride, titanium oxide, zirconium oxide, or mixtures thereof.23. An electrostatic chuck according to claim 18 wherein thesemiconducting dielectric comprises an electrical resistivity of fromabout 1×10¹⁰ Ωcm to about 5×10¹⁰ Ωcm.
 24. An electrostatic chuckaccording to claim 18 wherein the semiconducting dielectric comprisesaluminum oxide.
 25. An electrostatic chuck according to claim 24 whereinthe semiconducting dielectric further comprises at least about 8 wt %titanium oxide.
 26. An electrostatic chuck according to claim 18 whereinthe electrical isolator is adapted to reduce plasma formation in theconduit in a plasma environment.
 27. An electrostatic chuck comprising:an electrode; a first dielectric covering at least a portion of theelectrode and a second dielectric covering at least a portion of theelectrode; and at least one conduit extending through the electrode andan electrical isolator in the conduit.
 28. An electrostatic chuckaccording to claim 27 wherein the second dielectric extends around thefirst dielectric.
 29. An electrostatic chuck according to claim 27wherein the first dielectric material comprises an electricalresistivity of from about 5×10⁹ Ωcm to about 8×10¹⁰ Ωcm.
 30. Anelectrostatic chuck according to claim 27 wherein the second dielectricmaterial comprises a resistivity of from about 1×10¹¹ Ωcm to about1×10²⁰ Ωcm.
 31. An electrostatic chuck according to claim 27 wherein thefirst or second dielectric materials comprise aluminum oxide, aluminumnitride, silicon dioxide, silicon carbide, silicon nitride, titaniumoxide, zirconium oxide, or mixtures thereof.
 32. An electrostatic chuckaccording to claim 27 wherein one or more of the first or seconddielectric materials comprise aluminum oxide.
 33. An electrostatic chuckaccording to claim 32 wherein the first or second dielectric materialsfurther comprise at least about 8 wt % titanium oxide.
 34. Anelectrostatic chuck according to claim 27 wherein the electricalisolator is adapted to reduce plasma formation in the conduit in aplasma environment.